John Ostrom: The man who saved dinosaurs

Saw this on Facebook recently
The following is from an online Yale Alumni Magazine article (link below) by award-winning author, Richard Conniff, July/August 2014.

Preview
“In his book The Riddle of the Dinosaur, science writer John Noble Wilford added that Bakker “was the young Turk whose views could be dismissed by established paleontologists. Ostrom, however, could not be ignored.” Late in 1969, Ostrom took the challenge directly to the North American Paleontological Convention in Chicago, declaring in a speech that there was “impressive, if not compelling” evidence “that many different kinds of ancient reptiles were characterized by mammalian or avian levels of metabolism.” Traditionalists in the audience responded, Bakker later recalled, with “shrieks of horror.” Their dusty museum pieces were threatening to come to life as real animals.”

Figure 1. John Ostrom, from young paleo stud to elderly professorial type.

Figure 1. John Ostrom, as a young paleo stud and as an elder statesman several decades later demonstrating a degree of isometry and allometry during ontogeny.

“Against this false negative, Ostrom laid out the positive evidence, listing more than 20 anatomical similarities between Archaeopteryx and various dinosaurs. It wasn’t just that Ostrom could not be ignored. He was far too thorough and meticulous, and for 30 years too persistent in the face of his critics, for anyone to refute.”

The LRT has been online for only 8 years, so only 22 to go!

“Though one or two holdouts still resist the idea, it is now widely accepted that birds evolved from the group of bipedal theropod dinosaurs”

“The idea that birds are in fact living dinosaurs is so commonplace that the debate has largely turned to the question of why they were the only dinosaurs to survive the mass extinction of 65 million years ago.”

“More significantly, Ostrom lived to see his ideas about the dinosaur origin of birds—and the feathered plumage of dinosaurs—vindicated by a series of remarkable fossils from northeastern China.”

Those should have been unnecessary as Ostrom explains below.

“On Ostrom’s death in 2005, age 77, the Los Angeles Times wrote that he had “almost single-handedly convinced the scientific community that birds are descended from dinosaurs.” “John Ostrom,” the Sunday Times (London) added, “did more than anyone else to make dinosaurs interesting, real, and visceral.”

“When NPR’s All Things Considered marked the occasion by interviewing Ostrom’s first research student, Bob Bakker, the paleontological world held its breath for a moment, recalling the troubled relationship between these two allies in the dinosaur renaissance. But when asked how important Ostrom had been to dinosaur paleontology, Bakker graciously commented: “Nobody was more important.”

In the comments section to the online article,
you can read from Paul Sereno’s epitaph of Ostrom, “He did more than simply point out the great number of similarities between this theropod and the early bird Archaeopteryx. He argued that these similarities were derived. That is, that they were synapomorphies—shared morphology from common ancestry.”

We looked at Ostrom’s frustration with
the slow pace of paleontology earlier. Here it is again.

According to the Hartford Courant (2000), “In 1973, Ostrom broke from the scientific mainstream by reviving a Victorian-era hypothesis (see above) that his colleagues considered far-fetched: Birds, he said, evolved from dinosaurs. And he spent the rest of his career trying to prove it.” With the announcement of the first dinosaurs with feathers from China, Ostrom (then age 73) was in no mood to celebrate. He is quoted as saying, ““I’ve been saying the same damn thing since 1973, `I said, `Look at Archaeopteryx!’” Ostrom was the first scientist to collect physical evidence for the theory. Ostrom provoked a debate that raged for decades. “At first they said, `Oh John, you’re crazy,”’ Ostrom said in 1999.”

On the night Ostrom was to be honored
at the annual convention of the Society of Vertebrate Paleontology, I noticed him walking alone to the proceedings. I took advantage of the coincidence to walk with him. He was gracious enough to allow that. I cannot remember the substance of our conversation. As soon as we got to the building, he was swept up into the celebration as everyone else wanted their own moment with the man who saved dinosaurs.


References

https://pterosaurheresies.wordpress.com/2016/03/16/sometimes-it-takes-the-paleo-crowd-an-epoch-to-accept-new-data/

https://yalealumnimagazine.com/articles/3921-the-man-who-saved-the-dinosaurs?fbclid=IwAR1HMFU7cxeqn-iGd8dtO6nAxsjpERhyTza2AnpkCDz05k9fY3w-63-q4Wc

‘Prehistoric Life – Animated size comparison’ on YouTube

Figure 1. Click to enlarge. Pteranodon scene from Prehistoric Life video from Dane Pavitt. Incredible, excellent video, hearkening back to Giants of Land, Sea & Air - Past & Present (Peters 1986). Just a tweak or two necessary for the included Pteranodon. Extend those metacarpals and elevate that stance!

Figure 1. Click to enlarge. Pteranodon scene from Prehistoric Life video from Dane Pavitt. Incredible, excellent video, hearkening back to Giants of Land, Sea & Air – Past & Present (Peters 1986). Just a tweak or two necessary for the included Pteranodon. Extend those metacarpals and elevate that stance!

Another incredible YouTube video from animator Dane Pavitt!
Click below to view both of them.

I’m just nit-picking here…
In Dane Pavitt’s Pteranodon scene just a tweak or two is necessary to match the otherwise excellent presented data. Elongate those metacarpals and elevate that stance, as shown by the added Pteranodon data (Fig. 2). The small medial fingers, alas, could not contact the substrate (given available data), but this is one instance in which, perhaps, the big wing finger could. More likely Pteranodon was bipedal, only resting on its big wings.

Post-crania Pteranodon

Figure 2. Click to enlarge. Various Pteranodon specimens known from post-crania. Note the yellow box includes one of the largest specimens, but it has an unfused extensor tendon process, which may mean it is a very large Nyctosaurus with fingers.

Remember,
pterosaurs were bipeds originally and often. Typically pterosaur beach-combers and waders made quadrupedal tracks. They had different proportions. We have  bipedal tracks for the germanodactylid ancestors of Pteranodon.

Earlier (March 2016) Dane Pavitt premiered
an incredible march of dinosaurs video (click to view below) now with 17+ million views.

I’m delighted to see these videos
continuing and expanding in action and scope a concept presented in book form over 30 years ago (Peters 1986). I wonder if Dane Pavitt had a copy as a child.

References
Peters D 1986. Giants of Land, Sea & Air – Past & Present. A. Knopf. Click here to view.

Figure 1. The cover of Giants, the book that launched my adult interest in dinosaurs, pterosaurs and everything inbetween.

Figure 3. The cover of Giants, the book that launched my adult interest in dinosaurs, pterosaurs and everything in-between. Click to view and/or download the book.

Looking for a vestigial toe 5 on Jeholosaurus

Jeholosaurus is a small Early Cretaceous sister
to the Late Jurassic Chilesaurus and Late Triassic Daemonosaurus. All three nest as basalmost Ornithischia in the large reptile tree (LRT, 1399 taxa).

Phylogenetic bracketing indicates
a likely pedal digit 5 with a few phalanges should be found on all three taxa. Prior studies failed to reveal it. Current data does not include the pes for Daemonosaurus, nor show the ventral aspect of Chilesaurus, but Jeholosaurus does present the view we’re looking for (Fig. 1). I failed to notice pedal 5 before. I think others have overlooked it as well. Here it is:

Figure 1. Jeholosaurus pes in ventral aspect. DGS colors identify parts of pedal digit 5 disarticulated and broken on the sole of the foot and reconstructed at right.

Figure 1. Jeholosaurus pes in ventral aspect. DGS colors identify parts of pedal digit 5 disarticulated and broken on the sole of the foot and reconstructed at right. This observation is awaiting confirmation or refutation. Phylogenetic bracketing indicates this foot had a pedal digit 5 in vivo.

Finding pedal digit 5 on Jeholosaurus
was made a bit more difficult due to the vestige nature of the digit and its crushed and broken pieces, disarticulated from its traditional alignment lateral to pedal digit 4. This observation based on this photo awaits confirmation or refutation.


References
Han F-L, Barrett PM, Butler RJ and Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China. Journal of Vertebrate Paleontology 32 (6): 1370–1395.
Xu X, Wang and You 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4:)318-325.

wiki/Jeholosaurus
wiki/Daemonosaurus

 

 

New book encourages critical thinking in paleontology

Pagnac 2019 brings some fresh views to paleontology courses.
“University dinosaur courses provide an influential venue for developing aptitude beyond knowledge of terrestrial Mesozoic reptiles. Examination of dinosaur paleontology can develop competence in information analysis, perception of flawed arguments, recognition of persuasion techniques, and application of disciplined thought processes.
Three methods for developing critical thought are outlined in this book.
  1. “The first uses dinosaur paleontology to illustrate logical fallacies and flawed arguments.
  2. The second is a method for evaluating primary dinosaur literature by students of any major.
  3. The final example entails critique of dinosaur documentaries based on the appearance of dinosaurs and the disconnect between scientific fact and storytelling techniques.”

Students are owed more than dinosaur facts; lecturers should foster a set of skills that equips students with the tools necessary to be perceptive citizens and science advocates.”

Here at PterosaurHeresies
readers are also provided a set of skills and tools to illustrate logical fallacies and flawed arguments, evaluate and criticize with authority past and present paleo literature and challenge studies flawed by taxon exclusion.

Four questions:

  1. Do paleontologists engage with those critical of their favorite hypotheses?
  2. Do paleontologists ever accept (after rigorous testing) critical thinking that overturns their own pet hypotheses and/or traditional paradigms?
  3. Do paleontologists disrespect critical thinking if it comes from certain sources (ignoring the readily available data while doing so)?
  4. Are paleontologists ever annoyed by the achievements of others?
  5. All of the above?

Take your time in answering these.
Hopefully the Pagnac book will indeed encourage critical thinking. We looked at the lethargy that has always surrounded paleontology here.

References
Pagnac D 2019. Dinosaurs: A Catalyst for Critical Thought Elements of Paleontology

SVP 2018: The clade ‘Ornithoscelida’ tested

Mortimer et al. 2018
reevaluate taxa and scores for the proposed clade ‘Ornithoscelida’ (Baron, Norman and Barrett 2017) and find it less parsimonious than alternatives. The authors, “find hundreds of questionable scores, many characters are correlated with each other, score for multiple variables at once, or are formed in such a way that potential homology is masked.” 

After repairing scores,
the authors report, “none of these experiments supported Ornithoscelida over Saurischia.” Their results show:”that phylogenetic analysis of morphological data is highly vulnerable to typographic errors and other accidental, unsystematic misscores in data matrices; both quantity and quality of scores are important.”

We looked at
the Ornithoscelida hypothesis earlier here, here, here, and here. It is not supported by the large reptile tree (LRT, 1313 taxa, subset Fig. 1), which supports the hypothesis of a Theropoda-Phytodinosauria dichotomy splitting Dinosauria after the Herrerasaurus clade.

Importantly
the outgroup taxa to the Dinosauria must be recovered correctly. At present few to no other studies have included a robust selection of bipedal crocodylomorphs, which nest as the sister group to the Dinosauria in the LRT. Together only Dinosauria and Crocodylomorpha make up the Archosauria in the LRT.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria.

Scoring errors
are found in all (yes, all) phylogenetic analyses, including the LRT. One way to ‘eyeball’ whether an analysis is close to recovering actual evolutionary events is to look at every node for a gradual accumulation of derived traits. Key to this ideal is the inclusion of a sufficient number of relevant taxa. The LRT provides a good guide for taxon selection. As it grows larger it becomes a self-healing cladogram where imprecisely nested taxa reveal themselves. Some scores, when corrected, cement relationships. Other scores crack them apart.

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543:501–506.
Mortimer M, Gardner N, Marjanovic D and Dececchi A 2018. Ornithoscelida, phytodinosauria, saurischia: stesting the effects of miss cores in matrices on basal dinosaur phylogeny. SVP abstracts.

The many faces (and bodies) attributed to Camarasaurus

The genus Camarasaurus is known from several species
These display differences in the shapes of their skulls and post-crania (Fig. 1). Distinct from the bipedal or tripodal Diplodocus we looked at yesterday, the general build of this genus suggests it did not rise from all fours. Rather elevation of the great neck enabled high browsing, though not as high as its sister in the LRT, Brachiosaurus

Figure 1. Camarasaurus AMNH 567.

Figure 1. Camarasaurus lentus AMNH 567. Compare to shorter legged SMA 0002 specimen in figure 2.

Once considered a Camarasaurus,
the short-limbed, big pelvis Cathetosaurus (Fig. 2) is certainly related, but distinct from the other camarasaurs.

Figure 2. The SMA0002 specimen attributed to Camarasaurus.

Figure 2. The SMA0002 specimen attributed to Camarasaurus an/or Cathetosaurus. Note the robust elements and short distal limbs.

Not only are the bodies distinct,
so are the skulls (Fig. 3) assigned to this genus.

Figure 3. Several skulls attributed to Camarasaurus to scale. SMA 0002 is the short-limbed Cathetosaurus. Brachiosaurus appears to be a derived camarasaur.

Figure 3. Several skulls attributed to Camarasaurus to scale. SMA 0002 is the short-limbed Cathetosaurus. Brachiosaurus appears to be a derived camarasaur. We’re looking at the inside of the mandible in the DINO 2580 specimen.

As in many genera
for which several specimens are known, it is always a good idea to start with just one rather complete specimen in phylogenetic analysis. Add others as your interest grows.

References
Gilmore CW 1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah. Memoirs of the Carnegie Museum 10:347-384.
Madsen JH Jr, McIntosh JS, and Berman DS 1995. Skull and atlas-axis complex of the Upper Jurassic sauropod Camarasaurus Cope (Reptilia: Saurischia). Bulletin of Carnegie Museum of Natural History 31:1-115.
McIntosh JS, Miles  CA, Cloward KC and Parker JR 1996. A new nearly complete skeleton of CamarasaurusBulletin of the Gunma Museum of Natural History 1:1-87.
McIntosh JS, Miller WE, Stadtman KL and Gillette DD 1996. The osteology of Camarasaurus lewisi (Jensen, 1988). Brigham Young University Geology Studies 41:73-115.
Tschopp E, Wings O, Frauenfelder T, and Brinkmann W 2015. Articulated bone sets of manus and pedes of Camarasaurus (Sauropoda, Dinosauria). Palaeontologia Electronica 18.2.44A: 1-65.

Diplodocus joins the LRT

There are several ways to measure the tallest dinosaur.
One way is to let the long sauropods, like Diplodocus carnegii (Fig. 1; Marsh 1878; Late Jurassic; 25-32 m long), stand on their hind limbs, like their prosaurod ancestors, balanced by a very long narrow whiplash tail of up to 80 vertebrae. While the neck could not be elevated much beyond horizontal (relative to the dorsal vertebrae), by standing on its hind limbs the torso + neck could be elevated.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors. Diplodocus could potentially increase its feeding height up to about 11m

Wikipedia reports,
“No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus are well known.”

Figure 2. Diplodocus skull animation. Note the short chin and voluminous throat.

Figure 2. Diplodocus skull (USNM 2672, CM 11161) animation. Note the short chin and voluminous throat.

The peg-like teeth of Diplodocus
were smaller and fewer than in other sauropods. And the skull was smaller with nares placed higher on the skull. Evidently diplodocids could only handle smaller needles and leaves from conifer trees matching their height. Wikipedia reports, “Unilateral branch stripping is the most likely feeding behavior of Diplodocus.”

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

We know of junior diplodocids
(Fig. 5), half the skull length but with relatively larger eyes. Cute!

Figure 5. A small Diplodocus skull to scale with an adult one.

Figure 5. A small Diplodocus skull to scale with an adult one.

References
Marsh OC 1878. Principal characters of American Jurassic dinosaurs. Part I. American Journal of Science. 3: 411–416.

 

Sauropods as neotenous prosauropods

In the course of dinosaur evolution
sauropods reverted to quadrupedal locomotion, a trait found in embryo prosauropods, like Massospondylus, Fig. 1), but not in adult prosauropods or their dinosaurian ancestors.

FIgure 1. Massospondylus embryo in situ and reconstructed.

FIgure 1. Massospondylus embryo in situ and reconstructed.

This topic came to mind after seeing the new paper
on the Early Jurassic basal saurpodiform, Yizhousaurus (Zhang et al. 2018, which appears to remain bipedal as an adult; Fig. 2).

Notably, and despite it’s bipedal appearance,
in the large reptile tree (LRT, 1286 taxa), Yizhousaurus nests with the embryo Massospondylus (Fig. 1), not the adult (Fig. 4). Hence the title of this blogpost.

Figure 1. Yizhousaurus is an early Jurassic basal sauropod.

Figure 2. Yizhousaurus the early Jurassic basal sauropod that currently nests with the embryo Massospondylus.

Yes, the skeleton of Yizhousaurus
has much longer hind limbs than front limbs, which shows that the transition to a quadrupedal locomotion was gradual in adults, but the skull has several sauropod traits and the manual digit 1 ungual is no longer a big hook, but a stub, like the other manual unguals.

Figure 2. Skull of Yizhousaurus in several views.

Figure 3. Skull of Yizhousaurus in several views.

Sauropods like Yizhousaurus had their genesis
in the Early Jurassic and their greatest radiation in the Late Jurassic. Some clades extended to the Late Cretaceous.

FIgure 4. Massospondylus adult in situ.

FIgure 4. Massospondylus adult in situ.

Did sauropods have several or a single origin?
I have no idea, but the idea is already floating around out there.

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Carrano MT 2005.The evolution of sauropod locomotion: morphological diversity of a secondarily quadrupedal radiation.” in The Sauropods: Evolution and Paleobiology, edited by Curry Rogers, K. A. and Wilson, J. A., 229–251. University of California Press.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp.
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus PDF. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.
Zhang Q-N, You H-K, Wang T and Chatterjee S 2018. A new sauropodiform dinosaur with a ‘sauropodan’ skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China. Nature.com/scientificreports 8:13464 | DOI:10.1038/s41598-018-31874-9

wiki/Massospondylus
wiki/Yizhousaurus

You heard it here first: Daemonosaurus is an ornithischian

This one snuck under my radar
until Professor Thom Holtz mentioned it on the Dinosaur Mailing List. Writing about the Baron et al 2017 reply to Langer et al. we looked at earlier, Holtz wrote: “Novel discovery is Daemonosaurus as a basal ornithischian!!” (Fig. 1).

Actually that confirms a hypothesis of relationships
first recovered here back in 2011 when the large reptile tree (LRT, 1120 taxa) nested Daemonosaurus with the Ornithischia. So, the Baron et al. results confirm the earlier Peters 2011 discovery.

Figure 1. Here Daemonosaurus nests with basal ornithischians, not theropods, matching a nesting first recovered here in the LRT in 2011.

Figure 1. In Baron et al. 2017 Daemonosaurus nests with basal ornithischians, not theropods, matching a nesting first recovered here in the LRT in 2011.

As noted earlier, the Baron et al study is lacking a long list of pertinent taxa. Taxon exclusion is often the chief problem in phylogenetic analyses that rely on tradition.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale.

Figure 2. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale. These taxa nest together in the LRT.

Those who dislike the results recovered here
without a PhD and without seeing the specimens firsthand should note the growing list of taxa first recovered in the LRT that years later find confirmation in later studies by other workers.

References
Baron M.G., Barrett P.M. 2017 A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biology Letters 13, 20170220.
Baron MG, Norman DB and Barrett PM 2017.
 xxxx Nature 543501–506;  doi:10.1038/nature21700
Baron MG, Norman DB and Barrett PM 2017. Baron et al. reply. Nature 551: doi:10.1038/nature24012
Langer et al. (8 co-authors) 2017. Untangling the dinosaur family tree. Nature 551: doi:10.1038/nature24011

Origin of bipedalism in dinosaurs: Overlooking Carrier’s Constraint

Persons and Currie 2017 debunk on old theory
on bipedalism in dinosaurs and introduce a new one that suffers from taxon exclusion while overlooking a very popular theory from the last thirty years: Carrier’s Constraint (Carrier 1987).

From the abstract:
“Bipedalism is a trait basal to, and widespread among, dinosaurs. It has been previously argued that bipedalism arose in the ancestors of dinosaurs for the function of freeing the forelimbs to serve as predatory weapons.”

I never heard of this reason before. Predatory weapons only happen as a result and much later phylogenetically and only sometimes.

“However, this argument does not explain why bipedalism was retained among numerous herbivorous groups of dinosaurs. We argue that bipedalism arose in the dinosaur line for the purpose of enhanced cursoriality.”

The term ‘enhanced’ is pretty vague. Does it mean ‘better’? But can that be proven? The fastest animals on land now are quadrupedal cheetahs. Bipedal Chlamydosaurus does not have greater speed or endurance. Persons and Currie bring up the “tripping on one’s own forefeet” hypothesis and that, IMHO, has some validity.

“Modern facultatively bipedal lizards offer an analog for the first stages in the evolution of dinosaurian bipedalism. Many extant lizards assume a bipedal stance while attempting to flee predators at maximum speed.”

But quadrupedal lizards are just as fast as bipedal ones. Lizards gain no speed when switching to bipedal locomotion as Persons and Currie also note.

Bipedal lizard video marker

Figure 1. Click to play video. Just how fast can quadrupedal/bipedal lizards run? This video documents 11 meters/second in a Callisaurus at the Bruce Jayne lab.

“Bipedalism, when combined with a caudofemoralis musculature, has cursorial advantages because the caudofemoralis provides a greater source of propulsion to the hindlimbs than is generally available to the forelimbs.”

Yes, at first, especially when the forelimbs are lifted from the ground! Persons and Currie stay clear of the bipedal ability of fenestrasaurs including pterosaurs. There, in taxa like Cosesaurus, the driving force switches to the hips.

“That cursorial advantage explains the relative abundance of cursorial facultative bipeds and obligate bipeds among fossil diapsids and the relative scarcity of either among mammals.”

Actually there is no abundance of bipeds anywhere among diapsids, except in the Fenestrasauria (not related to archosaur-line diapsids) and Archosauria + Poposauria. Persons and Currie also stay clear of the inverted bipeds among mammals, the bats, and they are numerous.

None of the so-called ‘reasons’ why are pertinent
without the random evolution of longer hind limbs than forelimbs and the ability to balance over the hind limbs, whether running or standing still. It also helps to have even a small anterior addition to the ilium, according to Shine and Lambeck 1989. The pubic foot of theropods and the prepubis of pterosaurs also provide femoral muscle anchors.

Unfortunately

  1. Persons and Currie do not indicate the node at which bipedalism arose in the last common ancestor of bipedal crocs and dinosaurs: Gracilisuchus and Turfanosuchus at the base of the Poposauria. In the large reptile tree (LRT)  Gracilisuchus (Fig. is the last common ancestor of bipedal crocs, like Scleromochlus, and bipedal pro-dinosaurs, like Lewisuchus.
  2. Persons and Currie subscribe to the outdated hypothesis of “Avemetatarsalia” in which former members, like pterosaurs now nest with lepidosaurs and Lagerpeton now nests with chanaresuchids.
  3. Persons and Currie also avoid the likely bipeds, Arizonasaurus and Postosuchus.
  4. Persons and Currie discuss the the likely biped, Eudibamus, but incorrectly ascribe it to the bolosaurs.
  5. Persons and Currie overlooked Carrier’s Constraint, which holds that,“air-breathing vertebrates which have two lungs and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because the sideways flexing expands one lung and compresses the other, shunting stale air from lung to lung instead of expelling it completely to make room for fresh air.” — but is that the reason to go bipedal? or just the first and biggest advantage narrow-gauge bipedal reptiles enjoy?
Click to enlarge. Squamates, tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

Figure 2. Tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

What fenestrasaurs gain by a bipedal configuration

  1. height dominance over conspecific rivals for mating privileges. This is emphasized in Langobardisaurus with its long neck. This is emphasized by Cosesaurus by flapping and leaping, both working to increase height.
  2. Ability to breathe while running for added endurance
Chlamydosaurus, the Austrlian frill-neck lizard

Fig. 3. Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. At one time some paleontologists did not believe what you can see here, that this lizard can stand bipedally. Such was their bias.

What the lizard, Chlamydosaurus, gains by bipedal configuration

  1. combined with their frightfully opening frill neck, dominance over rivals and interlopers, which they charge bipedally.
  2. better ability to survey the local area for rivals (principally) and predators while on the ground, — but Chlamydosaurus is primarily (90%) arboreal for the same reason and 90% bipedal while on the ground, not just while running, which some paleontologists are not aware of or did not believe (Hone and Benton 2007, 2009).
Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

What Gracilisuchus gained by a bipedal configuration

  1. Gracilisuchus is not much taller bipedally. Remember, archosaurs had no scales at this point. Feather quills would appear on dino backs. Osteoderms appeared along croc backs to support their longer spinal columns. So, standing erect might have just been sexy at first.
  2. Overcoming Carrier’s Constraint: greater endurance by not having to undulate while breathing and so continue breathing while running.

What do bipedal reptiles have in common?

  1. Other than sauropods and other reptiles that adopt a tripodal pose bipedal reptiles are generally small, having experienced phylogenetic miniaturization.
  2. Other than Tanystropheus, bipeds are terrestrial and/or arboreal
  3. Longer hind limbs than forelimbs
  4. Anterior process of the illiim, no matter how small
  5. Typically stronger or more sacral connections to the ilium
  6. Typically a long neck and short torso (but Longisquama (Fig. 2), as a lemur analog, and lemurs themselves break that rule).
Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

It’s easy to overlook the most obvious.
I have a feeling that this will not be the first time Persons and Currie are going to be reminded of Carrier 1987.

References
Carrier DR 1987. The evolution of locomotor stamina in tetrapods: circumventing a mechanical constraint. Paleobiology (13): 326–341.
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